Thymectomized, lethally irradiated CBA mice reconstituted with anti-theta-serum-treated bone-marrow cells (TxB) were infected with T. spiralis at the age of 11 weeks. Intact, age-matched T. spiralis infected and non-infected CBA mice served as controls. Sera were collected up to 26 days after infection and examined for the presence of total and class-specific antibodies by indirect immunoflourescence. Mesenteric lymph nodes, spleen and axillary lymph nodes were examined by conventional histopathology for the presence of pyroninophilic blast cells, plasma blasts and plasma cells. Immunoflourescence was applied to examine cells containing immunoglobulins of various classes. Antibodies against T. siralis were demonstrated both in intact and TxB mice from day 10 after infection onwards. The amount of antibodies was lower in the TxB than in the intact mice. This might indicate that besides thymus-dependent, also thymus-independent antibodies against Trichinella are formed. No difference was observed in the thymus-independent areas of the lymphoid tissues from both intact and TxB mice, with the exception of a lower increase in number of IgM-containing cells in T cell-deprived mice. A marked increase in pyroninophilic blast cells was found in the thymus-dependent areas of the intact mice after infection, whereas only a very limited increase was observed in the T cell-deprived mice. The data were interpreted as supporting the thymus dependency of host response against Trichinella
